Bacterial Attachment, Aggregation, and Alignment on Subcellular Nanogratings

Engineering multifunctional surface topography to regulate multiple biological responses

Surface topography or curvature plays a crucial role in regulating cell behavior, influencing processes such as adhesion, proliferation, and gene expression. Recent advancements in nano- and micro-fabrication techniques have enabled the development of biomimetic systems that mimic native extracellular matrix (ECM) structures, providing new insights into cell-adhesion mechanisms, mechanotransduction, and cell-environment interactions. This review examines the diverse applications of engineered topographies across multiple domains, including antibacterial surfaces, immunomodulatory devices, tissue engineering scaffolds, and cancer therapies. It highlights how nanoscale features like nanopillars and nanospikes exhibit bactericidal properties, while many microscale patterns can direct stem cell differentiation and modulate immune cell responses. Furthermore, we discuss the interdisciplinary use of topography for combined applications, such as the simultaneous regulation of immune and tissue cells in 2D and 3D environments. Despite significant advances, key knowledge gaps remain, particularly regarding the effects of topographical cues on multicellular interactions and dynamic 3D contexts. This review summarizes current fabrication methods, explores specific and interdisciplinary applications, and proposes future research directions to enhance the design and utility of topographically patterned biomaterials in clinical and experimental settings.

Tailoring Cell Behavior and Antibacterial Properties on Zirconia Biomaterials through Femtosecond Laser-Induced Micropatterns and Nanotopography

This study explores the potential of ultrashort pulsed-direct laser interference patterning (USP-DLIP) to fabricate micropatterns on zirconia surfaces, aimed at enhancing their cell-instructive and antibacterial properties for biomedical applications. A femtosecond laser was employed to fabricate 3 and 10 μm periodic linear (L3 and L10) and grid (G3 and G10) patterns on tetragonal zirconia polycrystal stabilized with 3% molar yttrium oxide (3Y-TZP). The patterns exhibited homogeneous, high-aspect-ratio structures with laser-induced nanotopography within the grooves while maintaining minimal surface damage. All patterns significantly enhanced human mesenchymal stem cell (hMSCs) adhesion, spreading, and migration through topographical guidance and nanotopography-induced cell anchoring. Pattern geometry influenced cell morphology and migration: linear patterns induced high elongation and alignment along the grooves, leading to unidirectional migration, while grid structures promoted widespread cells with bidirectional alignment, promoting bidirectional migration. Antibacterial assessment using Pseudomonas aeruginosa (P. aeruginosa) (Gram-negative) and Staphylococcus aureus (S. aureus) (Gram-positive) revealed a size-dependent bacterial response. The patterns of lower periodicity (L3 and G3) showed superior antibacterial properties, reducing bacterial colonization through distinct mechanisms: mechanical trapping for P. aeruginosa (25% reduction) and disruption of bacterial aggregation for S. aureus (30% reduction). Coculture experiments with hMSCs and bacteria confirmed that L3 and G3 surfaces effectively combined enhanced cell adhesion with reduced bacterial colonization, highlighting the potential of USP-DLIP for developing multifunctional cell-instructive and antibacterial biomaterial surfaces.

Regulating Bacterial Culture through Tailored Silk Inverse Opal Scaffolds

Controlling the growth of microbial consortia is of great significance in the biomedical field. Selective bacterial growth is achieved by fabricating silk inverse opal (SIO) scaffolds with varying pore sizes ranging from 0.3 to 4.5 µm. Pore size significantly influences the growth dynamics of bacteria in both single and mixed-strain cultures. Specially, the SIO-4.5 µm scaffold is observed to be more favorable for cultivating S. aureus, whereas the SIO-0.3 µm scaffold is more suitable for cultivating E. coli and P. aeruginosa. By adjusting the secondary conformation of silk fibroin, the stiffness of the SIO substrate will be altered, which results in the increase of bacteria on the SIO by 16 times compared with that on the silk fibroin film. Manipulating the pore size allows for the adjustment of the S. aureus to P. aeruginosa ratio from 0.8 to 9.3, highlighting the potential of this approach in regulating bacterial culture.

Photocatalytic and antibacterial activity properties of Ti surface treated by femtosecond laser-a prospective solution to peri-implant disease

Laser texturing seems to be a promising technique for reducing bacterial adhesion on titanium implant surfaces. This work aims to demonstrate the possibility of obtaining a functionally orientated surface of titanium implant elements with a specific architecture with specific bacteriological and photocatalytic properties. Femtosecond laser-generated surface structures, such as laser-induced periodic surface structures (LIPSS, wrinkles), grooves, and spikes on titanium, have been characterised by XRD, Raman spectroscopy, and scanning electron microscopy (SEM). The photocatalytic activity of the titanium surfaces produced was tested based on the degradation effect of methylene blue (MB). The correlation between the photocatalytic activity of TiO2 coatings and their morphology and structure has been analysed. Features related to the size, shape, and distribution of the roughness patterns were found to influence the adhesion of the bacterial strain on different surfaces. On the laser-structurised surface, the adhesion of Escherichia coli bacteria were reduced by 80% compared to an untreated reference surface.

Highly active nanoparticle enhanced rapid adsorption-killing mechanism to combat multidrug-resistant bacteria

Contact-killing surfaces with the ability to rapidly adsorb and kill microorganisms are desperately needed since the rapid outbreak of multidrug-resistant (MDR) bacteria poses a serious threat to human health. Therefore, a series of amphiphilic nanoengineered polyquaterniums (ANPQs) were synthesized, and immobilizing ANPQs onto equipment surfaces provided a simple method for preventing microbial infections. The strong charge-positive property of ANPQ offered the possibility of rapid adsorption and efficient killing, such that all bacteria are adsorbed after 10 seconds of contact with ANPQ-treated fabrics, and more than 99.99% of pathogens are killed within 30 seconds. Surprisingly, the adsorption-killing mechanism made it difficult for bacteria to develop resistance to ANPQ coating, even after long-term repeated treatment. Importantly, in a Methicillin-resistant Staphylococcus aureus infection model, ANPQ-treated fabrics exhibited a potent anti-infectious performance while remaining nontoxic. It is envisaged that the strategy of using ANPQ coating undoubtedly provides a promising candidate for fighting MDR strains.

Fluid Flow Induces Differential Detachment of Live and Dead Bacterial Cells from Nanostructured Surfaces

Nanotopographic surfaces are proven to be successful in killing bacterial cells upon contact. This non-chemical bactericidal property has paved an alternative way of fighting bacterial colonization and associated problems, especially the issue of bacteria evolving resistance against antibiotic and antiseptic agents. Recent advancements in nanotopographic bactericidal surfaces have made them suitable for many applications in medical and industrial sectors. The bactericidal effect of nanotopographic surfaces is classically studied under static conditions, but the actual potential applications do have fluid flow in them. In this study, we have studied how fluid flow can affect the adherence of bacterial cells on nanotopographic surfaces. Gram-positive and Gram-negative bacterial species were tested under varying fluid flow rates for their retention and viability after flow exposure. The total number of adherent cells for both species was reduced in the presence of flow, but there was no flowrate dependency. There was a significant reduction in the number of live cells remaining on nanotopographic surfaces with an increasing flowrate for both species. Conversely, we observed a flowrate-independent increase in the number of adherent dead cells. Our results indicated that the presence of flow differentially affected the adherent live and dead bacterial cells on nanotopographic surfaces. This could be because dead bacterial cells were physically pierced by the nano-features, whereas live cells adhered via physiochemical interactions with the surface. Therefore, fluid shear was insufficient to overcome adhesion forces between the surface and dead cells. Furthermore, hydrodynamic forces due to the flow can cause more planktonic and detached live cells to collide with nano-features on the surface, causing more cells to lyse. These results show that nanotopographic surfaces do not have self-cleaning ability as opposed to natural bactericidal nanotopographic surfaces, and nanotopographic surfaces tend to perform better under flow conditions. These findings are highly useful for developing and optimizing nanotopographic surfaces for medical and industrial applications.

Tuning surface topographies on biomaterials to control bacterial infection

Microbial contamination and subsequent formation of biofilms frequently cause failure of surgical implants and a good understanding of the bacteria-surface interactions is vital to the design and safety of biomaterials. In this review, the physical and chemical factors that are involved in the various stages of implant-associated bacterial infection are described. In particular, topographical modification strategies that have been employed to mitigate bacterial adhesion via topographical mechanisms are summarized and discussed comprehensively. Recent advances have improved our understanding about bacteria-surface interactions and have enabled biomedical engineers and researchers to develop better and more effective antibacterial surfaces. The related interdisciplinary efforts are expected to continue in the quest for next-generation medical devices to attain the ultimate goal of improved clinical outcomes and reduced number of revision surgeries.

Bactericidal efficiency of micro- and nanostructured surfaces: a critical perspective

Micro/nanostructured surfaces (MNSS) have shown the ability to inactivate bacterial cells by physical means. An enormous amount of research has been conducted in this area over the past decade. Here, we review the various surface factors that affect the bactericidal efficiency. For example, surface hydrophobicity of the substrate has been accepted to be influential on the bactericidal effect of the surface, but a review of the literature suggests that the influence of hydrophobicity differs with the bacterial species. Also, various bacterial viability quantification methods on MNSS are critically reviewed for their suitability for the purpose, and limitations of currently used protocols are discussed. Presently used static bacterial viability assays do not represent the conditions of which those surfaces could be applied. Such application conditions do have overlaying fluid flow, and bacterial behaviours are drastically different under flow conditions compared to under static conditions. Hence, it is proposed that the bactericidal effect should be assessed under relevant fluid flow conditions with factors such as shear stress and flowrate given due significance. This review will provide a range of opportunities for future research in design and engineering of micro/nanostructured surfaces with varying experimental conditions.

Bacterial nanotubes mediate bacterial growth on periodic nano-pillars

Surface topography designed to achieve spatial segregation has shown promise in delaying bacterial attachment and biofilm growth. However, the underlying mechanisms linking surface topography to the inhibition of microbial attachment and growth still remain unclear. Here, we investigated bacterial attachment, cell alignment and biofilm formation of Pseudomonas aeruginosa on periodic nano-pillar surfaces with different pillar spacing. Using fluorescence and scanning electron microscopy, bacteria were shown to align between the nanopillars. Threadlike structures ("bacterial nanotubes") protruded from the majority of bacterial cells and appeared to link cells directly with the nanopillars. Using ΔfliM and ΔpilA mutants lacking flagella or pili, respectively, we further demonstrated that cell alignment behavior within nano-pillars is independent of the flagella or pili. The presence of bacteria nanotubes was found in all cases, and is not linked to the expression of flagella or pili. We propose that bacterial nanotubes are produced to aid in cell-surface or cell-cell connections. Nano-pillars with smaller spacing appeared to enhance the extension and elongation of bacterial nanotube networks. Therefore, nano-pillars with narrow spacing can be easily overcome by nanotubes that connect isolated bacterial aggregates. Such nanotube networks may aid cell-cell communication, thereby promoting biofilm development.

Bacterial Isolation Microwell-Plug (μWELLplug) for Rapid Antibiotic Susceptibility Testing Using Morphology Analysis

The rapid and accurate diagnosis of infectious diseases with high morbidity rates is crucial because it can minimize the misuse and overuse of antibiotics and increase survival rates in dreadful conditions. The conventional antibiotic susceptibility test (AST) systems used to choose appropriate antibiotics require long wait times to obtain results and cannot prevent the misuse or overuse of antibiotics by clinicians who need to quickly treat patients and cannot wait to identify the underlying cause of their symptoms. Therefore, several rapid AST (rAST) methods have been developed to provide quick test results, but they are complicated to operate, require additional equipment or materials, and give less accurate results than the conventional AST methods. In this study, we propose an rAST method that can obtain precise outcomes from a simple process with a short running time using a bacterial isolation microwell-plug (μWELLplug) in a conventional 96-well plate. The specifically designed hydrogel component of the μWELLplug provides a simple process for cell isolation and the observation of bacterial growth and morphological changes induced by a variety of antibiotic concentrations. The μWELLplug is placed over each well of the 96-well plate, and then bacterial or eukaryotic cells are isolated in the microwells and treated with different antibiotic concentrations to observe their effects. Saccharomyces cerevisiae (yeast, eukaryote), Streptomyces atratus (actinomycetes, prokaryote), Escherichia coli, Staphylococcus aureus, and methicillin-resistant S. aureus were cultivated and tested using the μWELLplug. The minimum inhibitory concentration values from this system were obtained in 3-4 h and correlated well with those from the conventional AST methods whose running time is 18-24 h.

The Effects of Subcellular Nanograting Geometry on the Formation and Growth of Bacterial Biofilms

Biofilm formation by bacteria protects them against environmental stresses such as desiccation, shear forces and antimicrobial agents, making them much harder to remove and increasing their virulence and persistence in industrial water systems and biomedical equipment. One promising method of disrupting biofilm formation and growth is to employ passive surface structures to inhibit bacterial adhesion and aggregation. However, most studies thus far have mainly focused on the early stages of biofilm formation and it is unclear if the influence of surface topography in the early phase will propagate to later stages. Here, we attempt to address this with an investigation into the biofilm formation of Pseudomonas aeruginosa on 25 different nanograting geometries, with dimensions that were systematically varied from subcellular to cellular sizes. The biofilms were characterized from the exponential growth phase to the decline phase, in intervals of 24 H over 4 days, using confocal scanning laser microscopy. Comparing the maximum volume of biofilm formed on each surface over 96 H, it was found that approximately 1/3 of the nanograting geometries exhibited 72 ± 16 % lower biovolume density than a flat surface. Bacteria on these nanogratings were also observed to form 40 ± 11 % smaller microcolonies that were 17 ± 6 % less compact than that found on the control surface. The majority of these nanogratings had deep trenches (i.e. depth ≥ 70% of the cell diameter). Furthermore, P. aeruginosa cells were observed to multiply at approximately twice the rate on almost all the nanogratings compared to flat surfaces, but these cell populations also began to decline 24 H earlier than those on a flat surface. Using available literature on P. aeruginosa, a qualitative model was put forth, attributing the results to increased cell motility, decreased exopolysaccharide formation and disrupted psl adhesin/signal trails on nanogratings. These factors, together, led to the net effects of reduced attachment, increased scattering of cells and rapid decline of the biofilms on nanogratings. The insights derived from this study suggest that passive surface geometries can be designed and optimized to successfully control/inhibit biofilm formation and growth.

Hierarchical Rose Petal Surfaces Delay the Early-Stage Bacterial Biofilm Growth

A variety of natural surfaces exhibit antibacterial properties; as a result, significant efforts in the past decade have been dedicated toward fabrication of biomimetic surfaces that can help control biofilm growth. Examples of such surfaces include rose petals, which possess hierarchical structures like the micropapillae measuring tens of microns and nanofolds that range in the size of 700 ± 100 nm. We duplicated the natural structures on rose petal surfaces via a simple UV-curable nanocasting technique and tested the efficacy of these artificial surfaces in preventing biofilm growth using clinically relevant bacteria strains. The rose petal-structured surfaces exhibited hydrophobicity (contact angle (CA) ≈ 130.8° ± 4.3°) and high CA hysteresis (∼91.0° ± 4.9°). Water droplets on rose petal replicas evaporated following the constant contact line mode, indicating the likely coexistence of both Cassie and Wenzel states (Cassie-Baxter impregnating the wetting state). Fluorescence microscopy and image analysis revealed the significantly lower attachment of Staphylococcus epidermidis (86.1 ± 6.2% less) and Pseudomonas aeruginosa (85.9 ± 3.2% less) on the rose petal-structured surfaces, compared with flat surfaces over a period of 2 h. An extensive biofilm matrix was observed in biofilms formed by both species on flat surfaces after prolonged growth (several days), but was less apparent on rose petal-biomimetic surfaces. In addition, the biomass of S. epidermidis (63.2 ± 9.4% less) and P. aeruginosa (76.0 ± 10.0% less) biofilms were significantly reduced on the rose petal-structured surfaces, in comparison to the flat surfaces. By comparing P. aeruginosa growth on representative unitary nanopillars, we demonstrated that hierarchical structures are more effective in delaying biofilm growth. The mechanisms are two-fold: (1) the nanofolds across the hemispherical micropapillae restrict initial attachment of bacterial cells and delay the direct contact of cells via cell alignment and (2) the hemispherical micropapillae arrays isolate bacterial clusters and inhibit the formation of a fibrous network. The hierarchical features on rose petal surfaces may be useful for developing strategies to control biofilm formation in medical and industrial contexts.

Investigation of Formation of Bacterial Biofilm upon Dead Siblings

Biocides can effectively kill bacteria; however, whether the dead bacterial cells left on the surface influence the later growth of biofilm is unknown. In this study, we have cultured Pseudomonas aeruginosa (PAO1) biofilm on their dead siblings and have investigated their evolution by using magnetic force modulation atomic force microscopy (MF-AFM). The time dependence of the biofilm thickness indicates that the deposited dead siblings can slow down the growth of PAO1 biofilm. The biofilm growing on dead bacteria layers is softer in comparison with those upon alive siblings, as reflected by the static elastic modulus ( E) and dynamic stiffness ( k_d) scaled to the disturbing frequency ( f) as k_d = k_d,0 f^γ, where k_d,0 is the scaling factor and γ is the power-law exponent. We reveal that the smaller population instead of the variation of extracellular polymeric substances (EPS) within the biofilm upon the dead siblings is responsible for the softer biofilm. The present study provides a better understanding of the biofilm formation, thus, making it significant for designing antimicrobial medical materials and antifouling coatings.

Micro- and Nanotopography Sensitive Bacterial Attachment Mechanisms: A Review

Bacterial attachment to material surfaces can lead to the development of biofilms that cause severe economic and health problems. The outcome of bacterial attachment is determined by a combination of bacterial sensing of material surfaces by the cell and the physicochemical factors in the near-surface environment. This paper offers a systematic review of the effects of surface topography on a range of antifouling mechanisms, with a focus on how topographical scale, from micro- to nanoscale, may influence bacterial sensing of and attachment to material surfaces. A good understanding of these mechanisms can facilitate the development of antifouling surfaces based on surface topography, with applications in various sectors of human life and activity including healthcare, food, and water treatment.